1. Field of the Invention
The present invention relates to an optical circuit design system for designing an optical circuit such as a silica- or LiNbO.sub.3 -based circuit, a semiconductor circuit, or MMIC (hereafter referred to as an "optical circuit") that is a circuit for propagating optical beams or microwaves, using the image processing of a computer, and to its image processing method and recording medium.
2. Description of the Prior Art
First, the characteristics of an optical circuit are described.
In an optical circuit, waveguides through which light propagates are generally formed on a planar substrate using a photolithographic process. Circuit elements formed can be classified into those which are functionally integrated (hereafter referred to as "functional circuit elements") and those which connect the functional circuit elements together (hereafter referred to as "wiring circuit elements"). The functional circuit elements implement functions such as optical branching, combining, filtering and switching and there are strong constraints among component graphics of these elements. The wiring circuit elements, however, have conditions such as the cross sectional shapes and refractive indices of the wiring waveguides, but their paths can be arbitrarily selected unless optical propagation loss can be maintained at a specified level.
The optical propagation loss depending on the shape of the optical waveguide can be classified into bending loss that depends on the curvature of the waveguide and transition loss that occurs at a position at which the curvature changes. Thus, with respect to the shape of the waveguide, a circular shape is more advantageous than shapes such as a spline, a Bezier curve, and a curve formed by combining trigonometric functions because its curvature remains unchanged to prevent transition loss. Consequently, the wiring circuit element often uses a combination of a straight line and a circular arc. The difference between the straight line and the circular arc can be neglected depending on the shape of the waveguide or the difference between a core and a clad in specific refractive index. In addition, in a wiring circuit element comprising a combination of a straight line and a circular arc, the straight line has a negligibly small optical propagation loss compared to the circular arc. Thus, such a wiring circuit element is normally evaluated using the radius and length of the circular arc. In a simpler form, such an element is designed so that the minimum radius of the circular arc has a specified value or larger.
Since the photolithographic process generally used in the LSI fabrication technique is used to produce an optical circuit as described above, a photomask to which a circuit pattern is transferred must be produced. Therefore, it is conventional to design an optical circuit or the like by inputting a circuit pattern with CAD, and editing the layout of circuit elements on the display screen.
The above optical circuit is characterized in that:
(1) curves are used as circuit elements, in that: PA1 a storage means for storing information of a correlationship which is previously determined and shows correlationship among line information showing shape of a graphic of composed of a straight line and/or a curved line, positions and direction of two end points of the graphic which represents the waveguide PA1 an indicator for indicating the positions and directions of said two end points in the form of the positions and the directions of the connection terminal of said part; PA1 an information processing means for obtaining the line information from the indicated positions and directions of the two end points based on the correlationship information stored in said storage device; PA1 and image processor for generating the graphic indicated by the line information obtained; and PA1 a display means for associating the generated graphic with the graphic of the part for display.
(2) the connections of the circuit elements and the layout of the overall circuit are essentially important because light propagates through the circuit, and in that: Thus, and optical circuit design system has the following performance requirements.
(a) The system can efficiently handle curves to be edited.
(b) The system can design the layout of the overall circuit easily.
In addition, since the integration and scale of optical circuits and the design time have recently been increased, it is efficient to reuse existing drawings. As a result,
(c) an optical circuit design system that effectively functions despite partial changes in the circuit is important.
Design systems used to design optical circuits to which this invention is applicable are used for LSIs, printed boards, machines, and civil engineering and construction. First, the current situation of such design systems and their applicability to the design of optical circuits are described.
Design systems for LSIs have already grown to a large technical field. Particularly, there have been many studies of the electric wiring method and many such methods have been put to practical use. The electric wiring in an LSI, however, comprises straight lines, wherein the intersections of the wiring are passed through throughholes to form a two-, three- or more-dimensional multilayer wiring. Thus, such a electric wiring is currently expressed as a one-dimensional layout and significantly differs from that in optical circuits that fundamentally prohibit intersections. Therefore, the design system for LSIs is difficult to apply to optical circuits. In addition, recent design systems for LSIs have an additional function for handling curves, but such a function simply inputs graphics of the elements of the circuit as parts and no such systems meet the performance (b) or (c) required for the optical circuit design system as described above.
The characteristics of design systems for printed boards are similar to those of design systems for LSIs but such systems do not include a layout wiring method that manipulates circular arcs frequently used in optical circuits.
Design systems for machines have a function for enabling the use of not only circular arcs but also curves such as splines and Bezier curves. In this sense, such systems can be used as design systems for optical circuits. Thus, the efficiency of inputting has been improved by using this method as a base and registering various standard circuit elements as parts beforehand. This is the current technical level on which optical circuits are designed. The conventional techniques, however, have the following problems with the edition of the layout of the overall circuit, as comprehensively described at the end of this section.
Some design systems for construction or civil engineering associate graphical elements with one another. For example, design systems are known which associate a graphic of a room with graphics of columns so that if the position of any column is changed, the shape of the graphic of the room is automatically changed. This association focuses only on particular graphic elements within the drawing and has objects different from those of the association between graphics which is used to lay out the overall drawing. This also means that required association depends on the shapes of graphic elements. In these points, these design systems cannot be applied to design systems for optical circuits easily.
An example of a method for designing an optical circuit using a design system for machines, which is currently most popular, and its problems are described below.
Current design systems for machines generally prepare functional circuit elements as standard circuit parts beforehand and inputs a layout by indicating the locations of these parts using a mouse. Wiring circuit elements (waveguides) are used to connect the laid-out parts together and drawn to design an optical circuit.
It should be noted that there are various constraints in connecting a waveguide between an output terminal of a circuit element and an input terminal of another circuit element. As an example of such constraints, light from an input terminal shall have a specific direction. As is apparent from FIG. 33, if a waveguide is connected which guides light from one circuit element 1000 to another circuit element 1007, it cannot be simply linearly connected.
More specifically, the direction 1003 of light from an output terminal of the circuit element 1000 must be aligned with the direction 1001 of light that passes through an optical waveguide 1004. To draw a connected waveguide that meets this constraint, the operator generates a circular arc with a certain curvature, connects one end of the circular arc to the output terminal of the circuit element 1000 in FIG. 33, and determines the position of the circular arc so that its direction is aligned with the direction of the output terminal. Likewise, a circular arc is connected to the other circuit element 1007. Finally, the ends of the two circular arcs are connected together by a straight line. In this case, the direction of the circular arcs must be aligned with the direction of the straight line.
In most cases, a single operation cannot successfully complete the drawing, and to complete the drawing, manual corrections must be provided by, for example, modifying the curvature or length of the circular arcs. Since whether the directions of the end of the circular arcs and the straight line are aligned is visually checked, an direction error may result when an optical circuit is really fabricated.
In addition, the end points of a circular circ have non-integers, so computations for the association for the position and direction of the end points are complicated. This is because current design systems do not include an established method for automating layout using publicly known circular arcs and splines.
In addition, the layout design of an optical circuit involves a large number of circuit elements and their positions must sometimes be changed during this process.
In such a case, the operator must re-connect the waveguide as described above, so the determination of the position of the waveguide has been a large problem in the design of optical circuits.
Finally, the problems with the prior art are listed.
Due to the lack of a method for automatically laying out graphics including curves (generally graphics comprising a group of multiple graphics) and an effective association method for compiling the layout of graphics including curves, current design systems input graphic elements independently of other already-input graphics while specifying their shapes, and associate only the graphic elements in part of the drawing with one another.
(a) Consequently, when part of the drawing is changed, the layout of at least all the adjacent graphics that must be inherently connected to that part or even the overall circuit must be changed, thereby requiring a large amount of time for edition.
(b) Due to the reason described in (a), it is often more efficient to generate a drawing by reusing existing drawings, so current design systems are wasteful in terms of the use of resources.